Heat exchanger for water heater

ABSTRACT

A heat exchanger for a water heater having a burner includes an outer tube extending longitudinally along a centerline from a first end adjacent the burner to a second end. Indentations are formed along the length of the outer tube and extend towards the centerline. An inner member extends through the outer tube and between the indentations such that flue gases from the burner flow in a passage between the inner member and the outer tube from the first end to the second end of the outer tube.

RELATED APPLICATION

This applications claims priority to U.S. Provisional Application Ser. No. 63/024,157, filed May 13, 2020, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to water heaters and more specifically to a flue tube heat exchanger for water heaters having enhanced heat transfer capability.

BACKGROUND

Storage type water heaters transfer heat primarily through the flue tube that runs through the center of the water tank. All of the flue tubes utilize some type of enhancement to extract heat from the flue gases passing therethrough. In one example, different types of baffles are employed to increase scrubbing of the flue tube walls to increase heat transfer. In another example, hundreds or even thousands of small metal tabs are welded to the inside walls of the flue tube to increase heat transfer. Each existing heat transfer enhancement can have inefficiency and/or cost issues.

SUMMARY

In one example, a heat exchanger for a water heater having a burner includes an outer tube extending longitudinally along a centerline from a first end adjacent the burner to a second end. Indentations are formed along the length of the outer tube and extend towards the centerline. An inner member extends through the outer tube and between the indentations such that flue gases from the burner flow in a passage between the inner member and the outer tube from the first end to the second end of the outer tube.

In another example, a heat exchanger for a water heater having a burner includes an outer tube extending longitudinally along a centerline from a first end adjacent the burner to a second end. Indentations are formed along the length of the outer tube and extend towards the centerline. An inner member extends through the outer tube from a first end positioned upstream of all the indentations to a second end aligned with the second end of the outer tube. The inner member extends between the indentations such that flue gases from the burner flow in a passage between the inner member and the outer tube from the first end to the second end of the outer tube. The indentations are arranged in pairs having the same longitudinal position and extending towards one another and towards the inner member.

Other objects and advantages and a fuller understanding of the invention will be had from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a water heater having an example flue tube heat exchanger.

FIG. 1B is an enlarged view of a portion of FIG. 1A.

FIG. 2 is a section view of the heat exchanger of FIG. 1A taken along line 2-2.

FIG. 3 is a top view of the heat exchanger of FIG. 1A.

DETAILED DESCRIPTION

The present invention relates generally to water heaters and more specifically to a flue tube heat exchanger for water heaters having enhanced heat transfer capability. Referring to FIG. 1A, a gas heated residential water heater 21 is shown and includes a water heating chamber 22 in which water to be heated (not shown) is stored.

A gas burner 18 is provided at the bottom of the water heater 21 behind a partition 23 in the water heater separating the gas burner from the heating chamber 22. An example heat exchanger 10 extends through the heating chamber 22 and is fluidly connected to the gas burner 18 at the bottom of the water heater 21 and an exhaust or vent system 25 at the top of the water heater.

The heat exchanger 10 includes a pair of members 12, 30 for transferring heat from the flue gases produced by the gas burner 18 to the water within the heating chamber 22. In the example shown, both members 12, 30 are tubes. The first or flue tube 12 extends longitudinally along a centerline 13 from a first/inlet end 17 or a second/exit end 19. The first end 17 extends through the partition 23 and is in fluid communication with the gas burner 18. The second end 19 is in fluid communication with the vent system 25. The first tube 12 can be formed from metal or any material having high thermal conductivity.

At least one parabolic shaped indentation 15 is pressed into the first tube 12 towards the centerline 13 to a depth necessary to provide a desired restriction. In the example shown, the indentations 15 can be pressed into the first tube 12 in pairs located diametrically across the tube from one another. In this configuration, confronting/opposing indentations 15 cooperate to define a dimple 20. The dimples 20 can be arranged such that a pair of dimples—and therefore four indentations 15—is provided at the same longitudinal position along the length of the first tube 12. The dimples 20 can be symmetrically arranged about the centerline 13 at the same location and collectively referred to herein as a “dimple set” for clarity. That said, the dimple sets can have the same rotational position relative to the centerline 13 as one another or different rotational positions. As shown, every other dimple set is rotated about 45° from the dimple sets on either side of it. Other rotational positions are contemplated.

In another example, a series of parallel planes extend through the first tube 12 along the length thereof (not shown). Each plane can include one or more of the indentations 15. Each plane can include the same number of indentations 15 of different numbers of indentations. The indentations 15 in each plane can confront one another or not confront one another and, thus, the indentation(s) in a plane may or may not form a dimple(s) 20.

The indentations 15 in each plane can be longitudinally aligned with the indentations in other planes or rotationally offset therefrom about the centerline 13. That said, the indentations 15 can be symmetrically or asymmetrically arranged about the centerline 13 in each plane and/or along the length of the first tube 12. The specific configuration and arrangement of the indentations 15 will depend on the desired operating parameter(s) of the heat exchanger 10.

The number of indentations 15 [and dimples 20, when present] used, as well as the exact shape of the indentations, can be adjusted to vary the restricting and turbulating characteristics of the first tube 12. Example configurations for the dimples 20 are shown and described in U.S. Patent Publication 2002/0005275, the entirety of which is incorporated herein.

The second member or tube 30 extends longitudinally along a centerline 32 from a first end 34 to a second end 36. The second tube 30 is positioned within the first tube 12. As shown, a bracket, e.g., a T-shaped bracket 41, is connected to the second end 36. In one example, the second end 36 is crimped (indicated at 39 in FIG. 1B) and secured to the bracket 41, which prevents fluid flow through the second end.

The legs of the bracket 41 are positioned on the second end 19 such that the second ends 19, 36 are longitudinally aligned. The first end 34 can terminate upstream of the furthest upstream indentation 15 in the first tube 12 and therefore be longitudinally spaced from the first end 17 of the first tube. Regardless, the centerlines 13, 32 are co-axial with one another.

The second member 30 is specifically configured to prevent fluid flow through the entire length of the second member. To this end, in lieu of or in addition to the crimped second end 36, the first end 34 can be closed in a fluid-tight manner. To this end, the first end 34 can be pinched/sealed or the second member 30 can be formed as a solid, elongated member without a central passage (not shown).

The second tube 30 can have any cross-sectional shape, e.g., round, circular, square, polygonal, etc. The indentations 15 of the first tube 12 extend towards the second tube 30 and can contact the exterior of the second tube, as shown in FIGS. 2-3. Contact between the indentations 15 and the second tube 30 helps to center the second tube within the first tube 12 and maintain with a co-axial relationship between the centerlines 13, 32. Alternatively, the indentations 15 can terminate in close proximity with the second tube 30 or be visibly radially spaced therefrom (not shown). In any case, a passage 40 is defined between the tubes 12, 30.

In operation, the gas burner 18 heats gases that move upward in the manner indicated by the arrows F through the partition 23 and into the passage 40 between the tubes 12, 30. The closed second end 36 and/or first end 34 of the second tube 30 ensures the heated gases can only flow through the passage 40 and not entirely through the second tube.

The heat from these gases F is conducted radially outward through the first tube 12 to heat the water in the water heating chamber 22. That said, the heated gases flow through the passage 40 and over/around the indentations 15, thereby greatly increasing the heat transfer through the first tube 12 and into the heating chamber 22. In any case, the heated gases flow the entire length of the passage 40 and are exhausted through the vent system 25.

Providing the combination of the indentations 15 and the second/inner tube 30 can allow for a lower pressure drop and better scrubbing of the side walls of the flue/outer tube 12. To this end, when the indentations 15 contact the second tube 30, the heated gases have a more tortuous path through the passage 40 and therefore have increased mixing and scrubbing of the wall of the first tube 12. Moreover, the indentations 15 reduce the volume occupied by the first tube 12 and therefore reduce the volume of the heat exchanger 10. This advantageously increases the volume of water that can be stored in the heating chamber 22.

What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. 

What is claimed is:
 1. A heat exchanger for a water heater having a burner, comprising: an outer tube extending longitudinally along a centerline from a first end adjacent the burner to a second end, indentations being formed along the length of the outer tube and extending towards the centerline; and an inner member extending through the outer tube and between the indentations such that flue gases from the burner flow in a passage between the inner member and the outer tube from the first end to the second end of the outer tube.
 2. The heat exchanger recited in claim 1, wherein the indentations are oval in the longitudinal direction of the outer tube.
 3. The heat exchanger recited in claim 1, wherein the indentations are parabolic in the radial direction of the outer tube.
 4. The heat exchanger recited in claim 1, wherein the inner member is a tube having a closed end for preventing flue gases from flowing through the inner member.
 5. The heat exchanger recited in claim 1, wherein the indentations are arranged in pairs having the same longitudinal position and extending towards one another and towards the inner member.
 6. The heat exchanger recited in claim 1, wherein the indentations are asymmetrically arranged along the outer tube.
 7. The heat exchanger recited in claim 1, wherein the indentations are spaced form the inner member.
 8. The heat exchanger recited in claim 1, wherein the indentations contact the inner member.
 9. The heat exchanger recited in claim 1, wherein the inner member and outer tube are concentric.
 10. The heat exchanger recited in claim 1, wherein the inner member extends from a first end positioned upstream of all the indentations to a second end aligned with the second end of the outer tube.
 11. A water heater including the heat exchanger recited in claim
 1. 12. A heat exchanger for a water heater having a burner, comprising: an outer tube extending longitudinally along a centerline from a first end adjacent the burner to a second end, indentations being formed along the length of the outer tube and extending towards the centerline; and an inner member extending through the outer tube from a first end positioned upstream of all the indentations to a second end aligned with the second end of the outer tube, the inner member extending between the indentations such that flue gases from the burner flow in a passage between the inner member and the outer tube from the first end to the second end of the outer tube, wherein the indentations are arranged in pairs having the same longitudinal position and extending towards one another and towards the inner member.
 13. The heat exchanger recited in claim 12, wherein the indentations are oval in the longitudinal direction of the outer tube.
 14. The heat exchanger recited in claim 12, wherein the indentations are parabolic in the radial direction of the outer tube.
 15. The heat exchanger recited in claim 12, wherein the inner member is a tube having a closed end for preventing flue gases from flowing through the inner member.
 16. The heat exchanger recited in claim 12, wherein the indentations are asymmetrically arranged along the outer tube.
 17. The heat exchanger recited in claim 12, wherein the indentations are spaced form the inner member.
 18. The heat exchanger recited in claim 12, wherein the indentations contact the inner member.
 19. The heat exchanger recited in claim 12, wherein the inner member and outer tube are concentric.
 20. A water heater including the heat exchanger recited in claim
 12. 